1. Field of the Invention
The present invention relates generally to molecularly imprinted polymers comprising chelated lanthanides and a process for preparing them.
2. Background of the Art
A number of organophosphorus compounds are used as pesticides and nerve agents. For example, organophosphorus based pesticides, including paraoxon, parathion and diazinon are widely used in the agriculture industry and the resultant environmental pollution is well documented. Because of their toxicity and relatively high solubility in water, organophosphorus based pesticides pose a clear threat to drinking water and aquatic life. It is therefore necessary to monitor the levels of these materials in industrial waste water, agricultural runoff, and other environments to determine compliance with federal and state regulations and other safety guidelines, as well as efficiency of wastewater treatments.
In addition, organophosphorus based nerve gases, including tabun and the organo-fluorophosphorus compounds sarin and soman, are of particular concern as chemical weapons which can be used on battlefields or by terrorists in civilian populated areas. Concerns over the use of these chemicals, as well as leakages from aging stockpiles prompt the development of easily used portable devices which can provide real time monitoring capabilities for such compounds.
Chemical sensors must fulfill two goals: (1) the development of a specific chemical recognition element that allows a molecule, or class of molecule, to be identified, and (2) a means of signal transduction in which the presence of the molecule causes a measurable change in a physical property of the material. Although these goals are not always separable, the successful design of chemical sensors requires that both be satisfied.
Most transduction approaches are based on optical, resistive, surface acoustic wave, or capacitive measurements. These well-developed methods dominate largely because of their ease of operation, sensitivity, and cost. The chemical recognition elements in these detectors, however, lag far behind. Indeed, most reports on chemical sensors suggest that many other devices could be fabricated if only suitable chemical recognition units were available. The missing element is a general approach to chemical recognition that allows the rational design and assembly of materials in a stable and reusable form. The present invention solves this problem based on the fabrication of molecularly imprinted polymers (MIPs).
An MIP is generally described as a plastic cast or mold of the molecule of interest, where recognition is based on shape, much like a lock and key. MIPs are made by adding the molecule of interest to a solution of binding molecules that can be chemically incorporated into a polymer. See FIG. 1. These binders usually have an affinity for the target and form a complex.
The interactions that hold these complexes together include π-π interactions, hydrogen bonding, metal-ligand binding, and even covalent bond formation, but they must be reversible. The binder must also have a chemical functionality that allows it to be irreversibly bound to polymers. Vinyl groups are a common functional group used to prepare many polymers, e.g., polyethylene, polystyrene, polyvinylalcohol, and polyvinylchloride. The target-binder complex is dissolved in excess matrix monomer (for example, styrene) and possibly other additives such as a cross-linker and porogens (solvents).
In a typical sensor fabrication, a solid plastic mass, consisting of the matrix and binder, is obtained which is chemically bound to the polymer/cross-linker matrix and the target molecule. Removal of the target is possible since it is reversibly bound to the binder. The cavity it leaves behind is permanently shaped like the target.
Sensors for organophosphorus compounds can be based on the luminescence of a lanthanide ion. See, for example, U.S. Pat. No. 6,749,811 B2, which is herein incorporated by reference. The process is enhanced when the lanthanide has sensitizing ligands. If the ligands can be polymerized a MIP sensor can be made. However, the best sensitizing ligands, such as β-diketones, may lose their ability to complex a lanthanide when a vinyl substitutent is added. Accordingly, what is needed is some other means for polymerization for making MIPs suitable for sensors.